Enthalpy in Changes of State

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Phase Change Noun

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[fayz cheynj]

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Phase Change

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A transition in the state of matter of a substance, occurring when heat addition or removal alters its particle arrangement.

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Example: This diagram shows that adding energy, like heat from a burner, causes matter to change its state (phase), such as solid ice melting into liquid water.

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Intermolecular Forces Noun

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[in-ter-muh-lek-yuh-ler for-sez]

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Intermolecular Forces

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The attractive or repulsive forces that exist between neighboring molecules, which are broken or formed during a phase change.

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Example: This diagram shows that the negative part of one water molecule attracts the positive part of another, creating an intermolecular force called a hydrogen bond.

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Intramolecular Forces Noun

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[in-truh-muh-lek-yuh-ler for-sez]

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Intramolecular Forces

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The forces, such as chemical bonds, that hold atoms together within a single molecule and are not broken during phase changes.

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Example: This diagram shows an intramolecular force as the strong chemical bond holding atoms together *within* a single molecule (like the solid line connecting Cl and H).

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Hydrogen Bonding Noun

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[hy-druh-jen bon-ding]

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Hydrogen Bonding

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A strong type of intermolecular force involving a hydrogen atom bonded to a highly electronegative atom like oxygen or nitrogen.

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Example: This diagram shows a hydrogen bond, a weak attraction between water molecules. Energy is needed to break these bonds, which is why it takes heat to change water's state.

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Heating Curve Noun

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[hee-ting kurv]

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Heating Curve

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A graph plotting a substance's temperature against added energy, showing plateaus that indicate a phase change is occurring.

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Example: This graph shows how a substance's temperature changes as energy is added, including plateaus where melting and boiling occur at constant temperatures.

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Enthalpy Noun

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[en-thal-pee]

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Enthalpy

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A thermodynamic property of a system that represents the total heat content, where its change indicates heat absorbed or released.

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Example: This diagram shows that adding heat energy (enthalpy) causes water to change state, from solid ice at 0°C to liquid water and then to gaseous steam.

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Kinetic Energy Noun

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[ki-net-ik en-er-jee]

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Kinetic Energy

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The energy that a substance's particles possess due to their motion, with the average being directly related to its temperature.

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Example: This diagram shows that particles in a gas have the most motion (highest kinetic energy), while particles in a solid have the least.

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Molar Enthalpy of Fusion Noun

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[moh-ler en-thal-pee uv fyoo-zhuhn]

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Molar Enthalpy of Fusion

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The amount of heat energy required to melt one mole of a solid substance into a liquid at a constant temperature.

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Example: This image shows ice melting in a drink. The ice absorbs heat energy from the drink to change from a solid to a liquid, a process called fusion.

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Molar Enthalpy of Solidification Noun

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[moh-ler en-thal-pee uv suh-lid-i-fi-kay-shuhn]

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Molar Enthalpy of Solidification

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The amount of heat energy released when one mole of a liquid substance freezes into a solid at a constant temperature.

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Example: This diagram shows energy being absorbed for melting (fusion). Solidification is the opposite: a liquid releases energy to freeze into a solid.

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Molar Enthalpy of Vaporization Noun

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[moh-ler en-thal-pee uv vey-per-i-zey-shuhn]

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Molar Enthalpy of Vaporization

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The amount of heat energy required to convert one mole of a liquid substance into a gas at a constant temperature.

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Example: This graph shows that as energy is added to a liquid, its temperature rises until it reaches the boiling point, where it vaporizes at a constant temperature.